A storage apparatus connected to a host computer via a network is equipped with, for example, a plurality of hard disk drives (HDD) as storage devices for storing data. When storing data in the storage devices, the amount of data is reduced and then stored in order to reduce costs of storage media. Examples of a method for reducing the amount of data include file compression processing and deduplication processing. The file compression processing reduces a data capacity by condensing data segments with the same content in one file. On the other hand, the deduplication processing reduces a total capacity of data in a file system or a storage system by condensing data segments with the same content detected in not only one file, but also in files.
A data segment that is a deduplication processing unit will be hereinafter referred to as a chunk. Also, logically gathered data that is a unit to be stored in a storage device will be hereinafter referred to as content. Examples of the content can include normal files as well as files such as archive files, backup files, or virtual volume files in which normal files are aggregated. Furthermore, chunks on which the deduplication processing has been executed are stored on a data block basis in the storage devices, wherein a plurality of chunks are gathered in data block units and each data block is called a container.
A specified number or capacity of chunks is set to a container in advance; chunks are gathered until the container becomes full; and once the container becomes full, the chunks are written on a container basis to the storage devices. Then, a container index table indicating which backup data is stored in which container is created in association with each container. For example, if backup data of a plurality of generations are deduplicated and stored in the storage devices, different containers are prepared for different backup generations depending on backup timing and the backup data of each generation is stored in each of the different containers (for example, see Patent Literature 1).